Frame flex?

I keep dropping my chain and yesterday I slammed my knee so hard onto my fork crown that I nearly picked my bike up and hucked it off a cliff. It's a 2012 Giant XTC 29er Aluminum frame and it flexes like a gay bodybuilder at a nude beach. The build is good with a Hive SS crankset and WI Eno Ecc rear hub and the Trials freewheel, bombproof. At first I thought it was the hub slipping so I sanded and knotched the dropouts just to be safe. Then I though it was my freewheel, which was a standard one but I replaced it with a $100 fancy schmancy WI trials one with 1 million teeth engagement and a rattlesnake inside. Then I thought it was the chain which was an 8-speed but I replaced it with the Sram singlespeed. Then I thought it was my alignment which was maybe .2 mm off so I went both ways with it a couple steps trying it after each and even put my chainring on the outside of the crank and tried that which was much worse. I got some custom shims and it's now maybe a red headed butt hair off at most! Basically, I've tried everything but replacing the frame. This entire build is only a few months old and less than 300 miles on it.

If I stand on the pedal with the front brake applied I can get the chain to loosen up and get about an inch and a half of freeplay. I can take it off the freewheel if someone is standing on it. I showed this to my LBS and they pretty much agree that the frame just can't handle single-speeding but they were also the ones who recommended this frame to me (which does handle amazing!). Now they are telling me to get a SC highball alu because it is intended for SS'ing but at this point i've lost some confidence in their opinion. They are going to sell me the highball at cost to make up for a bad recommendation which is cool of them but is that aluminum frame going to be any better? Are they full of ****? Do I just need to suck it up and get a steel/ti/carbon SS specific frame? Anyone want to buy a Giant XTC 29er M frame and an eccentric hub? Any good recommendations for a Medium 29er SS frame for a 100mm fork?

The SC frame might be a little better, but if I were in your shoes I would ditch the thought of aluminum. Steel is real, and it will give you the best bang for your buck, but carbon and Ti are both beautiful options also, if you've got the coin. Ti frames have been known to be a little noodly, though I have no experience with Ti so take that FWIW. As for a recommendation, I would go for a Salsa El Mariachi. Steel, great with 100mm fork, geo is dialed, alternator dropouts get rave reviews, and it won't break the bank. Niner SIR9 is another option with a little racier geometry, EBB, and slightly higher price tag. I don't know which would be closer in geometry to your Giant though.

What kind & size cog you riding? I had a problem awhile ago where I was vacationing I spent three days of riding and was so spent on the fourth day that I threw on my biggest cog which was a 21t from an old 8speed casset I took apart. the damn thing kept jumping off any time I hit a hill and had to push hard. Nothing would work to keep it on, later the following month I put it on again and it kept coming off no matter how tight or aligned the chain was but when I put any of the other single speed specific cogs on it worked fine and never came off. also note that it seemed to work fine when I used an 18t cog form the same old casset, so either the 21t cog was damaged or being a bigger tooth it was just enough flex to jump off a skinny short teeth cog. I do know most single speed cogs have longer teeth.

"Not drinking is the Single Speed World Championships version of doping" -Jacquie Phelan

If you are flexing off the rack Al, I don't think you'll fair any better with steel or Ti. Maybe if you went custom the builder could design more stiffness into the frame. I think your best bet is carbon.

Stiffness comes from design rather then material.

Steel, Aluminum, Ti, or Carbon can be made as stiff or flexible as the designer wants. In particular for a given tube diameter steel will be stiffer then aluminum or Ti. In order for an aluminum bike to be stiff the tubes need to be larger diameter because aluminum is not as stiff. Steel bikes with 42mm downtubes and oversized chainstays are crazy stiff.

With 29ers an added challenge is the tight area behind the bottom bracket where the rear tire, chainring, and chainstay all compete for space. If the cross section of the chainstay is reduced the bike will become more flexible unless an extra thick tube and/or a yoke is used the bike may lack stiffness.

You also may want to run a 22 tooth or larger rear cog and the corresponding chainring to make your existing and future bikes less susceptible to chain tension issues.

Iv'e got the exact same setup with no problems. Im running a 32-20 wi hubs and a wi freewheel 9 speed chain and a salsa ss chain ring. I did have my LBS custom build my wheels so im not sure if having the wheels dished for ss has anything to do with your issues. The guy who built my wheels really knows his stuff when it comes to custom setups like this. But i will take any pics of my rig that you need so we can compare and get to the bottom of this!

I just remembered that Wi has a funky chain line and When i was researching chain line i had to do something funky to make it work. It was something with spacers on the bb or. Ill take a look at my bike tomorrow.

Iv'e got the exact same setup with no problems. My chain fell off the first ride but i had the chain too loose and put it on a little tighter. I love the ride and the xtc just rails corners and climbs awesome! The geometry is perfect for me! I kinda wanna sell my lynskey and get the carbon xtc. Im running a 32-20 wi hubs with a wi freewheel and a 9 speed chain. I did have my LBS custom build my wheels so im not sure if having the wheels dished for ss has anything to do with your issues but i will take any pics of my rig that you need so we can compare and get to the bottom of this!

What crank are you running to get the chain line right for that WI hub?

Haha, that's funny, we have pretty much the same build. I'm running a 32-18. Yes I could alleviate all this by running a tensioner or one of those sliding chain guides but that would defeat the whole purpose of the eccentric hub and all the money I spent on it..and I don't like clutter, and I'm not going to run a 39t chainring so I can run a 22t freewheel, which would be another $100 just for the freewheel!

The flex is very noticeable on my frame at least, if you hold your front brake and pedal down how much slack can you put in the chain? I'll try to get a pic or something tomorrow to show but I go from really tight to REALLY loose, granted i'm built like a damn mule and put down some extreme torquage but I don't feel that should be happening regardless. I'm not necessarily opposed to "flex" but I am strongly opposed to chains coming off when I'm mashing up a hill. I dropped it off at the shop today and they are going to play with the alignment and test ride it tomorrow. I dropped off a 6 pack of some local DBA as well in case the test rider slams his face on the stem or his knee on the crown...or both. Hopefully I'll hear some good news like the alignment went out or something but I've pretty much concluded my investigations and am fairly certain it all comes down to frame flex. I hope not as I just built that damn thing but I can't see what else it would be. Here's mine (pic is old hub):

How many teeth do you have in the back/front? From the way it looks, that may be your problem. Put a 20 tooth or larger freewheel on and I bet your problems will be gone. You can run a larger chainring to give you the same effective gear. The larger your combo is the better your bike will do in terms of chain tension issues.

Also check your freewheel. I had an ACS freewheel on my first singlespeed and it was really bad with slop and play in the system. Compared to a WI freewheel or a normal cassette hub the cheap china made freewheel was penny wise and pound foolish because it wore out in a matter of weeks.

How many teeth do you have in the back/front? From the way it looks, that may be your problem. Put a 20 tooth or larger freewheel on and I bet your problems will be gone. You can run a larger chainring to give you the same effective gear. The larger your combo is the better your bike will do in terms of chain tension issues.

Also check your freewheel. I had an ACS freewheel on my first singlespeed and it was really bad with slop and play in the system. Compared to a WI freewheel or a normal cassette hub the cheap china made freewheel was penny wise and pound foolish because it wore out in a matter of weeks.

Slow down and the read the thread. OP's last post answered your first question. His original post already mentioned he's running a WI trials with a gazillion points of engagement. There is zero wrong with his freewheel.

I had problems before with an ebb where I sized the chain wrong on install because I wasn't thinking about the ebb. Another time with different gear combo on the same bike with the ebb it just wouldn't work with the gearing I chose. I had to choose between a half link or leaving the chain where it was at and installing a new front ring + one tooth. I chose changing the front ring +1 to a 33.

I understand that you are not currently running that hub but in the pic the chain is SUPER loose to me. Maybe just a mock up or pre-adjustment in the pic and that's fine, but if your chain still looks like that you've found at least one problem.

As I said, that's an old pic, I've since updated both the chain and freewheel. I played with the alignment a little and got the chain tight, zero slack. I'm going to go for a couple hour ride and see what happens, hopefully I don't smash my nuts.

Did you put a SRAM PC-1 chain on there? If so, that is the most elastic chain I've ever used. Try a KMC chain double check the chainline....

That is bs. Whatever problems the OP is having a KMC chain sure isn't going to fix. That chain looks way loose in one of the pics but like SS said I've run them like that and still never dropped a chain.

Seems weird but it does seem like something is up with that frame, especially since the shop agreed and it seems like Free Coffee checked most of the other boxes.

I'm not saying that the chain couldn't be the problem, just that it isn't a brand problem.

I dunno. I used to love the PC-1 chain until I started having chain drop problems. I have track fork ends, and I kept tightening the chain but it would always pop off. It got so bad I had to tighten the chain after every ride. I switched to KMC and it works a lot better (for me). Chain hasn't popped off in over 600 miles.

Another problem could be your front chain ring. If you pedal backwards, does the chain maintain its tension consistently? Are there loose spots then tight spots? That could cause the chain to pop off as well. You may need to re-align your front chain ring. You will never get it "perfect", but it could help. Large differences in tension could be the cause.